Reflecting electric lamp



June 11, 1940.

C. BIRDSEYE El '1 REFLECTING ELECTRIC LAMP Filed Nov. 25, 1938 114 U6 11W0 2 deg/1444c 162L411? Patented June 11, 1940 UNITED STATES REFLECTINGELECTRIC LAMP Clarence Birdseye and Pincus Deren, Gloucester, Mass.,assignors, by mesne assignments, to

Birdseye Electric Corporation,

Gloucester,

Mass., a corporation of Massachusetts Application November 25, 1938,Serial No. 242,216

6 Claims.

The present invention relates to electric lamps and consists in animproved reflecting lamp having certain advantages over those heretoforeavailable. The invention includes within its scope the process hereindisclosed of producing such improved reflecting lamp. In reflectingelectric lamps in which the light source is hooded by a reflectingsurface formed upon the bulb there is a tendency for the reflected raysto project a shadow of the mount and filament supports or an image ofthe incandescent filament and to produce thereby a light pattern that isirregular in intensity and unpleasant to the eye. Heretofore thisobjectionable tendency has been eliminated to some extent by frostingthe transmitting area of the bulb either on the inside or the outside.The frosted transmitting area diffuses the light emitted by the bulb soas to eliminate or largely reduce uneven light intensity patterns caston the illuminated area.

There is however a serious objection incident to the practice abovediscussed. When practically all the light rays from the incandescentfilament are directed by the reflecting surface through the transmittingarea of the bulb the concentration of light is so great that the glassof the bulb in this area, when frosted in the usual commercial manner,becomes intensely brilliant. This frosted transmitting area even becomesso bright that, particularly in lamps of high wattage, it is unpleasantto observe directly despite the fact that the filament may be completelyhooded by the opaque reflecting portion of the bulb. In fact a lampfrosted for direct illumination inthe customary manner when viewed fromthe side is very much brighter throughout its tfinsmitting area than asimilar lamp without any frosting.

In our prior Patent No. 2,144,673, granted January 24, 1939, of whichthe present application is a continuation as to all common subjectmatter, We have disclosed a method of preventing the formation ofshadows and bright images in the illuminated areas by applying adiffusing reflector to the surface of the bulb. In one aspect thepresent invention consists in an improvement over that disclosed in oursaid prior patent. viz. we control the diffusion of the reflected lightby a combination of two cxpedients each however modified to an extentthat would make either of them alone inadequate for the purpose, and

- which at the same time, avoids certain very real the entire innersurface of the bulb is processed so that it presents a continuouscontour of smooth shallow rounded depressions, the reflecting coatingbeing applied to this surface in the desired areas as metal deposited orevaporated directly upon the processed surface of the bulb and therebygiven a diffusing reflecting characteristic. The configuration impartedto the bulb by the suggested treatment is hardly adequate to give to themetal deposited upon it a pronounced difiusing character sufiicient toeliminate shadows, nor will the same treatment of the transmitting areaaccomplish this end by itself. However, by combining the diffusingreflecting surface thus produced and the diffusing transmitting surfacein cooperative relation, so that their individual effects are additive,the final result is highly satisfactory in eliminating shadows in theilluminated area. Moreover, this is accomplished without causing thetransmitting area to glow with a high degree of brilliancy. Further, theprocessed transmitting area diverts but a slight amount of light ascompared to the amount which is lost in a corresponding area which hasbeen commercially frosted and there is practically no loss of lightwithin the lamp at any point of diffusing reflection since the metalliccoating preferably may be applied to the inner surface of the bulb sothat no loss occurs on account of the passage of light through the-glassto and from an exterior reflecting surface.

Our invention includes within its scope a novel andimproved process ofproducing the reflecting bulb above discussed. The process of ourinvention is characterized by first processing the inner surface of thebulb in the manner described, then applying a metallic reflectingcoating to the internal processed surface and finally removing the metalcoating by means of a chemical solution to define a transmitting area inthe lamp. Heretofore it has been the general practice when applyingareflecting coating of silver or aluminum to the internal surface of lampbulbs to coat sub-' in the case of silver coating or caustic soda in thecase of aluminum coating.

These and other features'and characteristics of our invention will bebest understood and appreciated from the following description of onemanner of practicing the process of our invention and an illustrativeexample of a reflecting electric lamp embodying our invention. In thedrawing- Fig. 1 is a view in elevation, with parts broken away,suggesting the step of depositing a metallic reflecting coating upon theinner surface of a processed bulb, and includes a section of the bulbwall as seen magnified approximately 500 times in the fleld of amicroscope;

Fig. 2 is a similar view suggesting the step of removing the metalliccoating from the transmitting area of the coated bulb, and

Fig. 3 is a view in elevation of the complete lamp, and also includes asection of the bulb wall as seen in the field of a microscope.

The first step in the process of our invention is to providesubstantially the entire inner surface of the bulb with a particularconfiguration of contour which, for want of a better term, we will calla shell surface. By this we mean a contour of shallow roundeddepressions or hollows which covers substantially the whole surface, andhas no deep valleys, no sharp peaks and no flat facet faces, but merelygently scooped and rounded depressions. The individual depressions orhollows are of varied size, irregular in shape and appear to be boundedby straight or slightly curved lines extending in all direction andmeeting in vertices sometimes in pairs and sometimes in greater numbers.In Fig. 1 the characteristic surface is represented as actually observedin the field of a microscope at a magnification of 300 to 500.Heretofore frosting imparted to bulbs has been characterized by deepcavities with steep sides which under the microscope look in some placeslike the facets of crystals and in other places present sharply concavesurfaces. These actually act to reflect the light back and forth fromside to side of the pits or cavities and create much greaterdisturbances and absorption of the light than does the type ofconfiguration employed in accordance with our invention. Our novelconfiguration of surface, on the contrary, does not substantiallyinterfere with the directional characteristics of the lamp, that is tosay, the reflecting surfaces of the lamp define the beam in which thelight is emitted and the reflecting or diffusing effect of the shellsurface is not such as to deflect any substantial amount of lightoutside this beam. The effect we desire is a slight differentialrefraction of the light passing through the transmitting section of thebulb in a heterogeneous manner, that is, the

emergence angle 'of each ray is only slightly different from thestraight line it would follow in emerging from an unprocessed bulb.

The present commercial process of frosting bulbs is fully disclosed inU. S. Letters Patent No. 1,687,510, October 16, 1928, Pipkin. Theprocess of that patent involves the use of two' different frostingsolutions of the same composition, the

second used being merely weaker than the first.

' from any frosted surface known before our discovery and as suchconstitutes an important aspect of our invention.

Having first provided the desired shell surface in the bulb, the nextstep of the process is to apply a metallic reflecting coating thereto.One process of applying such metallic coating is dis closed in ourcopending application, Ser. No. 191,493, filed-February 19, 1938. InFig. 1 is illustrated the step of vaporizing silver or aluminum to forma reflecting coating in the manner more fully disclosed in our saidapplication. The processed bulb I is inverted over a pair of electrodesH and i2, sealed and exhausted. Between the electrodes is mounted a boator receptacle l3 in which is placed a charge of metal for the coating.The exhausted bulb is heated and the metal charge reduced to a moltenstate while the bulb is maintained under vacuum so that any gasesevolved from the metal charge are immediately removed from the bulb. Thecharge in the boat I3 is then quickly raised to the vaporizing point ofthe metal by electrical energy transmitted to the electrodes H and I2.The metal is thus flashed and deposited upon the shell surface of theinner walls of the exhausted bulb.

In this operation a diffusing reflecting surface is formed of thegeneral character disclosed in our prior Patent No. 2,144,663 alreadyidentified. The'structure of this reflecting surface is indicated inFig. 3 of the drawing from which it will be seen that the gently slopingrounded hoilows and depressions of the shell surface are now coated witha thin deposit of metal l9 thereby forming a reflector which is mildlydiffusing, that is to say, in which the reflected rays are slightly butnot violently deflected from the normal paths which they would follow ifspecularly reflected from the surface of unprocess walls. Our object isto provide a reflecting surface having a relatively slight diffusingaction which is combined in its effect with the relatively slightdiffusing action of the shell surfaced transmitting portion of the lamp.The cooperative effect of these two factors produces the desired resultsin eliminating shadows and bright images in the area illuminated by thelamp.

The next step in our process consists in removing the reflecting coatingfrom a selected area of the bulb to define a shell surfaced transmittingportion therein. The metallic coating may be removed in accordance withthe process of our prior application, Ser. No. 177,780, filed Decem her2, 1937. In that process a solvent solution is applied to those portionsof the bulb from which it is desired to remove the metallic coating. Wehave suggested in Fig. 2 the step of removing metallic coating from thebowl end of a bulb intended for use in direct lighting. The coated bulbIll is supported in upright position and the solvent solution issupplied through a vertical tube l5 surrounded by a larger tube orcasing l6 and containing concentrically a smaller withend of the tubel'l within the delivery tube l and acts to prevent splashing of thesolvent solution as it is supplied to the bulb up to substantially thelevel of its maximum diameter. If silver is employed as a coating forthe bulb an acid solution, such as nitric acid, may be delivered throughthe tube 15. If aluminum is used as the metal of the coating a stronglyalkaline solution may be similarly employed. As soon as the coating isdissolved the solution is withdrawn through the innertube l1 and thebulb immediately washed out, with the result that a sharp line ofdemarkation is formed between the silver coating [9 and the bare shellsurfaced transmitting portion 20 of the bulb.

Having completed the shell processing and metallic coating of selectedareas of the bulb in the manner above explained the bulb may now beemployed in the manufacture of an electric reflecting lamp by followingthe conventional steps of manufacture. The mount 21 and filament aresealed into the bulb neck with the filament substantially hooded by thereflecting coating i9. Preferably the filament will be of the coiledcoil type supplying a concentrated light source. The bulb is thenexhausted, gas filled if desired, and sealed preparatory to beingequipped with a metal base 22- of any desired commercial construction.It will be understood that the shallow rounded depressions making up'the shell surface of the bulb are actually infinitesimal in size. Theprocessed surface is of a somewhat lustrous light gray or pearl color inappearance and noticeably more transparent than a frosted surface. Thesurface as illustrated in Figs. 1 and 3 is' drawn from microphotographstaken at a magnification of 500 diameters and then enlarged in thereproduction. In addition to providing an electric reflecting lampsupplying a substantially uniform light pattern and one in which thetransmitting portion of the "lamp is not objectionably brilliant whenthe lamp is in use, we have substantially increased the illuminatingefliciency of the lamp by reducing the amount of light absorbed anddiverted in its transmitting portion as compared with lamps heretoforecommercially available. The intensity of illumination derived from alamp constructed in accordance with our invention is about 16% greaterthan that derived from a commercially frosted lamp of identical size andrating.

I While it is not practicable completely to remove a metallic coatingfrom a shell surface by mechanical means, it is possible by using ascraping tool to form a translucent spiral or other markings in thecoated area of a bulb processed as herein disclosed if it should bedesired to secure the luminous appearance of the coated portion of thebulb as disclosed inthe prior patent of Birdseye, No. 2,074,888, March23, 1937.

Having thus described our invention what we claim as new and desire tosecure by Letters Patent of the United States is,

1. A reflecting electric lamp comprising a bulb having an interiorsurface with a shell configuration of contour, a metallic coatingcovering portions of said surface and presenting a roughened diffusingreflecting surface which limits and defines a shell surfacedtransmitting area in the bulb, and a light source hooded within thereflecting area.

2. A reflecting electric lampcomprising a light source and a bulb havinga diffusing metallic reflecting surface, in combination with a diffusingtransmitting portion in the bulb, neither of which processed to presentshallow rounded concavities contiguous to each other and ofinfinitesimal size, a metallic coating covering a portion of theprocessed surface and presenting a diffusing reflector for concentratingand directing the light of the lamp in a beam, and defining by its edgesan uncoated processed transmitting area through which the light beam isdirected and by which its rays are slightlydiffused without pronouncedillumination of the glass of said transmitting area.

4. A reflecting incandescent lamp comprising a bulb having a shellsurface partly coated with a metallic reflector and uncoated in atransmitting' area, said lamp providing a practically shadowlessillumination substantially 16% more intense than a lamp otherwisesimilar but with a commercially frosted transmitting area.

5. A glass electric lamp bulb having its entire interior surface frostedby etching so that the maximum brightness of an ordinary incandescentlamp comprising such a bulb will be more than twenty-five per cent ofthat of said lamp with a clear bulb, said interior bulb surface beingcharacterized by the presence of shallow as distinguished frompronounced depressions and having a reflecting metallic coating upon aportion of said surface and rendered diffusive thereby,

and an uncoated transmitting portion.

6. An electric incandescent lamp having a glass bulb provided with ashell surface, that is to say, a glass surface which when observed at amagnification of 800 to 500. appears to comprise shallow roundedcontiguous depressions or hollows, varied in size. irregular in shapeand bounded by slightly curved and straight lines extending in alldirections and meeting at vertices sometimes in pairs and sometimes ingreater numbers, and. a metallic reflecting medium applied as a coatingof substantial thickness to said shell surface thereby presenting adiffusing reflecting surface in the lamp. I

CLARENCE BIRDSEYE.

PINCUS DEREN.

